1. Field of the Invention
This invention relates to the field of marking. More specifically, the invention comprises a system for projecting an illuminated line on a floor. The line may serve to guide automated vehicles, to segregate one area from another, and for many other purposes.
2. Description of the Related Art
A line placed on a floor surface can serve a wide variety of purposes. A simple use for such a line is separating two areas. An example of this would be identifying a boundary between an area where fork trucks are allowed to operate and another area where they are not. In recent years, lines placed on a floor surface have also been used to define a route for an automatically guided vehicle (“AGV”).
AGV's routinely handle transport tasks in modern factories. Many AGV's are equipped with a forward and downward facing optical system that is able to track a contrasting line placed on the floor. Other marking may be used to identify “stops” that an AGV makes. “Stops” may also be identified using radio frequency or other signals.
Many methods are used to place lines on a floor surface. Paint-based striping machines, similar to those used on roadways, can accurately place a painted line. In more recent years, however, the lines are created using a specialized tape. The tape includes an adhesive on one side, allowing it to be stuck to the floor. A non-linear path may be created by splicing together linear portions. Some tapes can even be laid in a curved path, provided that the radius of curvature is not very small.
The tapes themselves fall into two broad categories. The first category is based on magnetism. These tapes include a ferromagnetic substance. A magnetic sensor on the AGV provides steering input on the basis of its proximity to the tape. Magnetic tapes may even include differently-polarized sections allowing the implementation of other features.
The second category is based on optical contrast. Such tapes usually provide a bright and/or reflective surface that contrasts with a background surface. An example is a bright yellow tape placed on a dull concrete surface. The AGV includes a light source and an optical sensor that “sees” the contrast between the tape and the background surface and uses this value to guide the AGV's steering.
The use of optical tape has well known disadvantages. The tape of course resides on the factory floor, where it is subjected to a punishing volume of traffic. The tape may become scuffed and torn. In prolonged use it may simply wear through in sections. The solution to these problems is to periodically renew the tape. Many users lay multiple tape layers on the same path until the height of the tape becomes a problem. Then the entire “stack” is removed, the surface is cleaned, and a new initial layer of tape is laid. This is a time consuming and labor intensive process.
It would therefore be desirable to provide a guidance method that allows the use of existing AGV guidance hardware but eliminates the known disadvantages of the prior art optical tapes. The present invention provides such a solution.